Well, it happened. A truly epic late-season snowstorm walloped the Southern Willamette Valley Sunday night and Monday, knocking out power to tens of thousands of people and bringing over a foot of snow to Eugene and over twice that to Bend. Even Portland saw flurries for much of the day, with locations above 500 feet picking up an inch or two of snow. Additionally, models and forecasters did a fantastic job with this storm, hopefully regaining the public’s trust after some of our botched snow forecasts earlier this month!
Credit: NWS
Storm totals generally ranged from a trace-3 inches for the Portland metro area, with the highest amounts in the higher elevations west of downtown. Salem and Corvallis both saw a couple inches, but totals really picked up once you headed south of Corvallis. Eugene saw a foot, Cottage Grove saw over 14 inches, and there was a report of 18 inches 2 miles west of Creswell at 880 feet. Snow totals were absolutely ridiculous east of the Cascade Crest; Bend and Redmond saw 2-3 feet in 24 hours. Click here for a list of snow totals throughout Western Oregon and the Willamette Valley, and here for totals in Eastern Oregon. Sunday morning’s University of Washington’s WRF-GFS model absolutely nailed the distribution and amount of snowfall with this system.
As I’ve touched on in previous blogs, this snowstorm actually had subtropical origins. A deep upper-level trough in NE Pacific pumped mild, moist air near the Hawaiian Islands towards the West Coast, while a separate trough off the Washington/Oregon Coast allowed cold air to surge south from British Columbia into the Pacific Northwest. This resulted in an extremely strong front, with warm/moist air to the south of the front and cold, dry air to the north. Places just to the north of this front saw the magic combination of near-freezing temperatures and subtropical moisture, resulting in extraordinary amounts of wet, heavy snow.
Credit: University of Washington
The “sounding” below (soundings are vertical profiles of the atmosphere and are generally measured with a radiosonde, or weather balloon) was taken at Salem at 4 am Monday, and it shows how the atmosphere was both cold and moist (the green line measures the dewpoint; note how closely it follows temperature). Weather soundings are not taken at Eugene, but if they were, I expect you’d see something similar to this but with even more moisture and perhaps slightly warmer temperatures. The combination of cold temperatures and this amount of moisture is very hard to come by in the Pacific Northwest, but when you get both, you can get an incredible amount of snow.
Credit: Storm Prediction Center
The combination of deep moisture throughout the atmosphere and near or slightly above-freezing temperatures ensured that this snow was extremely wet and heavy. Taking a look at observations at Eugene Airport, I believe that their 12-inch snowfall corresponded with 1.71 inches of liquid precipitation, meaning that there was a 7:1 snowfall-to-liquid ratio. Most snow:liquid ratios are closer to 10:1, and this ratio often exceeds 30:1 when the air is extremely dry and cold. The Wasatch Mountains of Utah commonly get such ratios when they experience lake-effect snow off the Great Salt Lake, making for incredible powder skiing. There’s a reason why the 2002 Winter Olympics were hosted in Salt Lake City.
The weight of all this snow brought down trees and power lines and even caused some light property damage. Eugene Water and Electric (EWEB) had over 13,000 of their ~86,000 customers without power at one point.
Over 13k customers still w/o power. We had significant damage to the electric system & tree limbs are still coming down. Crews are out assessing, responding to downed power lines, & focusing on restoration. We will be working through the night to help as many people as possible. pic.twitter.com/nriX0XExqb
— EUG Water & Electric (@EWEButility) February 26, 2019
Due to colder temperatures, the snow was lighter and fluffier in Bend, but they saw over twice the amount of snowfall that Eugene did. From what I’ve heard, power outages weren’t as widespread, but snow-covered roads made for treacherous travel conditions… provided you could get to your car in the first place, of course.
Had to dig out the rig! #bend @mtbachelor #gnargnarpowpow pic.twitter.com/fAwswbNeHv
— BK (@bkolp) February 27, 2019
Rain and Flooding
With the South Valley snow getting so much attention, it’s easy to forget about the flooding and mudslides that occurred due to heavy rain on the southern side of both Sunday night/Monday’s storm and another system currently affecting the West Coast, which I’ll get to in just a bit. The heaviest precipitation was focused between Eugene and San Francisco, with North/Central California experiencing the heaviest rain. There are widespread 5-10+” totals along the immediate coast, Coast Range, Klamath Mountains, and Sierra Nevada, with much less but still significant precipitation in the Central Valley. These systems have dropped incredible amounts of snow in the Sierras – by Thursday morning, parts of the Sierras will have seen 10 feet of snow since Saturday.
Credit: NWS
One thing that caught my eye was the tremendous gradient in precipitation across the Golden Gate bridge. Downtown San Francisco has seen half an inch of rain over the past 72 hours, while the mountains just to the north saw 5-10 inches. This shows how much terrain can enhance precipitation and how sharp the dividing line between light and heavy precipitation can be – two defining characteristics of relatively stationary atmospheric rivers like this one.
A plethora of rivers in North-Central California are currently experiencing flooding, and Cache Creek (NW of Sacramento along I-5) is “above danger stage.” Yikes!
Snow Tonight:
After such a historic storm, it’s easy to forget that more snow is actually in the forecast for the Willamette Valley tonight!
Credit: NWS
From a meteorological perspective, this storm is similar to Sunday night/Monday’s, with a developing wave of low pressure along an atmospheric river lifting a band of snow north through the Willamette Valley. However, the bulk of precipitation is over North/Central California, and Eugene will not see a foot of snow from this system… perhaps 2-4 inches instead. Note how the heaviest precipitation is just to the north of San Francisco.
Credit: NWS
If you look closely, you’ll see that there is a huge gap in radar coverage over SW Oregon. It has been incredibly frustrating to have such poor radar coverage throughout these series of storms, and these storms have shown us how important that we get a coastal radar for Oregon, similar to the one we got up at Langley Hill in Washington. This blog is long enough and that’s a topic for another post, but in the meantime I encourage you to like the “Oregon Coast Radar Committee” page on Facebook to get the latest updates on the progress being made towards getting a coastal radar.
Finally, here’s a snow forecast from the Portland NWS, because it’s getting late and I am too tired to make my own. These amounts seem reasonable based on current radar/observations. I doubt regions close to the Columbia River Gorge will see much accumulating snow at all due to cold, strong, dry easterlies there that allow snow to sublimate before it reaches the ground. The morning commute might be a little slippery in spots for those in the SW metro, but I don’t expect too many impacts elsewhere in the Portland metro area. Expect the strong Gorge easterlies to die down by mid-morning tomorrow, and with highs rising into the upper 30s, the evening commute should be fine.
Credit: Portland NWS
Thanks so much for reading, and enjoy what will likely be the last accumulating snow of the season for the Willamette Valley, unless we get really lucky with some heavy pre-dawn showers early Friday morning.
Charlie
